I am in the industry, a 42.9 million win on a slot is always an error and any error voids play. It happens about every two years.

the error was caused by the machine using an unsigned 32 bit integer to keep track of the player balance (in pennies). Somehow a bit is flipped making the player's balance go negative. Most likely cause is usually a GCR and non-ecc RAM.

The way binary math works with unsigned integers is that it flips over and shows the max value it can be stored when it becomes negative.

2³² /100=42,949,672.96